Despite the many advancements in the audio arts, reinforcement systems commonly fail to satisfy at least some portion of a serious audience. Such failures are not always due to basics such as insufficient gain or audio power capability and/or inferior or defective components such as microphones, amplifiers and loudspeakers: even with equipment components of excellent quality, capable of delivering adequate levels of gain and acoustic power, these capabilities often cannot be effectively realized because of a more subtle and complex limitation: positive acoustic feedback from the loudspeaker(s) to the microphone(s) reaching the threshold of instability corresponding to unity overall loop gain. The excessive unnatural reverberations and other distortions heard as this threshold is approached, and even worse, the uncontrolled acoustic "howl" that results when the threshold is exceeded, are common experiences, typically associated with unsuccessful efforts to adjust the system to remedy inadequate coverage of some portion of the audience.
In a typical scenario which is especially prone to such feedback problems, a loudspeaker is located to the rear of the stage, behind the lecturer, facing the microphone; such a set-up may result either from inexperience or from worthy intentions of having the reinforced sound originate from a location near the lecturer, since intuitively this would seen desirable. The capability and coverage of such a system would be severely limited by acoustic feedback.
Efforts to overcome such feedback problems have led to two general approaches:
(1) locating the loudspeaker at a long distance away from the microphone; while this approach helps to mitigate feedback, the perception of a "disembodied" amplified voice, typically much louder than the lecturer's own voice, originating from somewhere other than from the lecturer's location, is distracting and tends to strain the audience's attention;
(2) utilizing multiple loudspeakers at various locations throughout the audience; this approach can be effective in covering a large audience more completely, however the source displacement cited for approach (1) tends to compound to a further distracting confusion or loss of source localization for much of the audience, and a further loss of intelligibility may occur due to destructive standing wave patterns set up by interferences between two or more separated loudspeakers. Over long distances, as in large halls or worship places, or outdoors, arrival-time differences at listerners' ears can destroy intelligibility.
Acoustic feedback is strongly related to the directional properties of the microphone(s) and/or loudspeaker(s) in the system, in combination with their relative locations. Selecting both the microphone(s) and the loudspeaker configuration for special directional properties holds promise in addressing the problem of acoustic feedback while avoiding harmful side effects; however the potential benefits depend not only on judicious selection of directional components, but just as importantly on determining and maintaining optimal deployment. Failure to fulfill the potential benefits of directional components, even when well selected, is commonly caused by improper location of the components relative to each other and to the environment: a temporary of flexible setup is subject to location variations caused by operator inexperience or haste, while a fixed permanent installation may perpetuate improper locations.
Generally, it would be desirable to locate a speaker unit near the front of the stage; however, usually other stage usage requirements preclude a permanent or fixed installation at a preferred onstage location.